Men with prostate cancer who are treated with testosterone-lowering drugs are twice as likely to develop dementia within five years as those whose hormone levels are not tampered with, researchers including one of Indian origin have found.

Testosterone can promote the growth of prostate tumours, and so clinicians have used androgen deprivation therapy to lower testosterone and other androgens in prostate cancer patients since the 1940s.

The team at the Stanford University and the University of Pennsylvania in the US looked at deidentified records for nearly 10,000 patients with prostate cancer.

Out of the 1,829 who received androgen deprivation therapy, 7.9 per cent developed dementia within five years, compared with 3.5 per cent of those not treated with ADT.

"The risk is real and depending on the prior dementia history of the patient we may want to consider alternative treatment, particularly in light of recent study," said Nigam Shah, associate professor at Stanford.

The study tells that prostate cancer patients randomised to either active monitoring, surgery or radiation therapy all had the same risk of death from the cancer after 10 years.

Ninety-nine per cent of men in the study survived regardless of initial treatment. These startling results suggest that active monitoring of prostate cancer patients may be as good as early radical treatment and may cause fewer side effects.

The actual number of patients possibly at risk for dementia from androgen deprivation therapy is small, it makes sense when weighing the value of prescribing ADT to try to identify which prostate cancer patients might be vulnerable to dementia, said Shah.

The study adds to a growing body of evidence supporting Stanford Medicine's precision health approach, the goal of which is to anticipate and prevent disease in the healthy and precisely diagnose and treat disease in the ill.

"I was surprised at how ubiquitous the effects on all types of dementia were, but I would definitely not alter clinical care based on our results," said lead author Kevin Nead, from University of Pennsylvania.

He added that he would like to see a prospective, randomised clinical trial to establish whether ADT can be more firmly linked to an increased risk of dementia and to help identify what kinds of patients might be vulnerable to that increased risk.

He anticipates that checking for dementia risk in people treated with ADT will be part of future randomised, clinical trials that have a larger focus.

The study was published in The New England Journal of Medicine.

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